# type-fest — Essential TypeScript Utility Types Collection

> A curated collection of essential TypeScript types covering objects, strings, arrays, JSON, and more, maintained by Sindre Sorhus with strict typing guarantees.

## Install

Save in your project root:

# type-fest — Essential TypeScript Utility Types Collection

## Quick Use
```bash
npm install type-fest
```
```ts
import type { PartialDeep, ReadonlyDeep, SetRequired } from 'type-fest';

type Config = { db: { host: string; port: number } };
type PartialConfig = PartialDeep<Config>;
// { db?: { host?: string; port?: number } }
```

## Introduction
type-fest provides a curated, well-tested collection of TypeScript utility types that fill gaps in the built-in utility types. Maintained by Sindre Sorhus, it covers deep partial, readonly, JSON types, string manipulation, and dozens more patterns commonly needed across TypeScript projects.

## What type-fest Does
- Provides deep recursive versions of built-in types like PartialDeep and ReadonlyDeep
- Offers strict variants of Extract, Exclude, and Omit that catch typos at compile time
- Includes JSON-related types for parsing and serialization safety (JsonValue, JsonObject)
- Supplies string literal manipulation types like CamelCase, KebabCase, and Split
- Adds array utilities like FixedLengthArray, ArraySlice, and LastArrayElement

## Architecture Overview
type-fest is a pure type-level library with zero runtime code. Each type is defined in its own source file, tree-shakeable by design. The library requires TypeScript 5.9 or later and strict mode enabled. Types are organized by category and exported from a single entry point for convenient imports.

## Self-Hosting & Configuration
- Install via npm: `npm install type-fest`
- Import types using `import type` syntax only (no runtime footprint)
- Requires `strict: true` in tsconfig.json
- Requires TypeScript 5.1 or later (5.9 recommended for latest features)
- Works with any bundler or runtime since it emits no JavaScript

## Key Features
- Over 200 carefully designed utility types
- Zero runtime overhead since every export is a pure type
- Strict mode variants that enforce exact key matching
- Extensive JSDoc documentation with inline examples for every type
- Battle-tested across thousands of npm packages

## Comparison with Similar Tools
- **ts-toolbelt** — larger library with 300+ types; heavier, more complex API surface
- **utility-types** — smaller collection focused on mapped and conditional types; less maintained
- **ts-essentials** — overlapping scope with deep partial and readonly types; fewer string utilities
- **TypeScript built-in utilities** — Partial, Pick, Omit, etc.; lacks deep variants and string types
- **simplytyped** — lightweight alternative; discontinued

## FAQ
**Q: Does type-fest add any runtime code to my bundle?**
A: No. Every export is a TypeScript type, removed entirely during compilation.

**Q: Which TypeScript version is required?**
A: TypeScript 5.1 or later with strict mode enabled. Some newer types require 5.9.

**Q: Can I use individual types without importing the whole package?**
A: Yes. Use `import type { CamelCase } from 'type-fest'` and your bundler will include only the type reference, which compiles away.

**Q: How is PartialDeep different from the built-in Partial?**
A: The built-in Partial only makes top-level properties optional. PartialDeep recursively makes every nested property optional as well.

## Sources
- https://github.com/sindresorhus/type-fest
- https://www.npmjs.com/package/type-fest

---
Source: https://tokrepo.com/en/workflows/asset-4e847fd4
Author: AI Open Source